A 71-yr-old woman with a widely metastatic lipidrich variant of breast cancer was found to have striking hyperamylasemia (85-fold normal). By isoelectric; focusing, agarose gel electrophoresis, and a wheat protein inhibitor assay, the predominant serum amylase appeared to be identical to pancreatic isoamylase. Serum trypsin, serum lipase, and an abdominal computed tomography scan were normal, excluding the possibility of pancreatitis. Furthermore, both the primary breast tumor and skin metastases that developed 10 yr later stained immunohistochemically for amylase. Thus, breast carcinoma must be added to the list of tumors causing ectopic hyperamylasemia, and this case shows that nonpancreatic malignancies may produce pancreatic-type hyperamylasemia.